Anionic nucleotide--lipids for in vitro DNA transfection.

A family of new anionic nucleotide based lipids featuring thymidine-3'-monophosphate as nucleotide and 1,2-diacyl-sn-glycerol as lipid moiety for in vitro delivery of nucleic acids is described. The nucleotide lipids were prepared in three steps starting from 1,2-diacyl-sn-glycerols and 2'-deoxythymidine-3'-phosphoramidite. Gel electrophoresis experiments show that nucleotide-based lipid-DNA complexes are observed at Ca(2+) concentration higher than 1 mM. The transfection experiments carried out on mammalian Hek cell lines clearly demonstrate that the nucleotide moiety enhances the transfection efficacy of the natural anionic DPPA and DPPG lipids. SAXS studies indicate that the enhancement in transfection for nucleotide-based lipid formulations compared to those of the abasic natural derivative (DPPA) is likely due to the presence of the 2D columnar inverted hexagonal phase (H(II)) with a unit cell parameter a = 69.1 A in the nucleotide lipid formulations. The cytotoxicity studies of lipoplexes, evaluated against Hek cells using an MTS assay, revealed that palmitoyl nucleotide derivative complexes were not toxic even after 4 h of incubation, thus indicating that the anionic nucleotide lipids presented in this work offer an alternative to cationic transfection reagents.